Safety control system for cooling a gas turbine power plant on shutdown



Nov l1, 1952 G. R. FusNER Erm.

SAFETY CONTROL SYSTEM FOR COOLING A GAS TURBINE POWER PLANT ON SHUTDOWN4 Sheets-Sheet l Filed Sept. 23, 1950 QQQQ QM.

nm s a Tw oPJ. t. non eea Vim. Urp eh GC Nov. ll, 1952 G. R. FUSNER ETALSAFETY CONTROL SYSTEM FOR COOLING A GAS TURBINE POWER PLANT oN sHuTDowNFiled sept. 23, 195o 4 SheetsSheet 2 NNN The` Attorneg.

Nov. M, 1952 G. R. Fu? SAFETY CONTROL SY T TURBINE POWER PLANT ONSHUTDOWN NER ETAL 2,617,253 EM FOR COOLING A GAS 4 Sheets-Sheet 3 FiledSept. 23. 1950 Nov. 1l, 1952 G. R. FUSNERv E'r AL SAFETY CONTROL SYSTEMFOR COOLING A GAS TURBINE POWER PLANT ON SHUTDOWN 4 Sheets-Sheet 4 FiledSept. 23, 1950 I LS EQ um Nu bbl Inventors mf?, um ee. D H. m T a Pw .TO.J A Rn O. r @a *.l @The o@ T eh GC patented Nov. 11, 1952 UNITED STATESSAFETY CONTROL SYSTEM FOR COOLING A GAS TURBINE POWER PLANT` ON SHUT-DOWN George R. Fusner and Chapman J. Walker, Schenectady, N. Y.,assignors to General Electric Company, a corporation of New YorkApplication September 23, 1950, Serial No. 186,354

(Cl. Sti-39.09)

11 Claims.

This invention relates to a method and apparatus for governing theoperation of a gas turbine powerplant, particularly regulating means forthe starting and stopping cycles thereof.

This invention was developed specifically in connection with a 5,000 kw.gas turbine powerplant having a plurality of heat exchangers ofsubstantial size and mass for removing heat from the fluid during thecompression process, transferring heat from the turbine exhaust gas tothe combustion air, etc. A serious problem encountered in the design ofsuch a powerplant results from the very substantial heat storagecapacity of the heat exchangers. If special provision is not made forsafely disposing of this stored heat, there is a substantial risk that,after shutting down the powerplant, currents of air from the surroundingatmosphere will blow back down the exhaust stack, pick up heat in theheat exchangers, and enter the compressor, which has blades of magnesiumor aluminum alloy, or other similar materials not able to withstand theresulting high temperatures. For instance, this blow-back may easilyresult in gases of a temperature on the order of 800 F. reaching thecompressor blades, with extremely serious damage to the blading, warpageof the entire compressor rotor structure, and perhaps damage to thebearings. This stored heat will also have a tendency to warp the turbineand compressor casings, frame structure and bearing supporting members,with the result that excessive deformations may take place in the rotorand frame structure.

Accordingly, the object of the present invention is to provide animproved regulating system for a gas turbine powerplant, speciallyarranged to remove the heat stored in the heat exchangers and other hotcomponents by turning the compressor rotor for a certain period aftershutdown so as to cause comparatively cool air from the atmosphere tocirculate through the compressor, then through the heat exchangers,combustion system and other hot components, for such period of time asmay be required to blow out the stored heat. In a large powcrplant ofthe type described, this may take as long as 6 hours, and during thisperiod the continuous rotation of the turbine-compressor rotors insuresthat they will cool evenly.

Other objects and advantages will become apparent from the followingdescription taken in connection with the accompanying drawings, in whichFig. 1 is a schematic View of a simple gas turbine powerplant having asingle regenerative heat exchanger for transferring waste heat in theexhaust gases to the combustion air, and having a representativeregulating system arranged in accordance with the invention; Fig. 2 is adetail View illustrating the type of clutch employed between thestarting motor and the gas turbine rotor; Fig. 3 is a diagramrepresenting the sequence of operations during the starting and thestopping and cooling cycles; Fig. 4 is a diagrammatic outline of a morecomplex gas turbine powerplant having a control system in accordancewith the invention; and Fig. 5 is an operating diagram for thepowerplant of Fig. 4.

Generally, this invention is practiced by manually or automaticallyre-energizing the auxiliary starting motor, after the powerplant hasbeen shut down by discontinuing the fuel supply thereto, and causing thepovverplant rotor to turn continuously at such a speed and for such a,length of time as may be required, to circulate air throughout thepowerplant so as to carry away the stored heat.

Referring now more particularly to Fig. 1, the gas turbine powerplant,illustrated diagrammatically, comprises a multi-stage compressor,preferably of the axial-How type, shown at l, a combustion systemindicated at 2, the turbine proper shown at 3, and a heat exchanger darranged as a regenerator for transferring heat from the hot gasdischarged from turbine 3 to the combustion air as it flows fromcompressor l to combustion system 2. It will be apparent that theaxialow compressor l has an inlet casing la and a discharge casing ib,and is connected to the regenerator by a transition conduit 5. Theregenerator in turn communicates by way of conduit with the inlet to thecombustion system 2, from which the hot gases pass directly through theturbine wheel. Waste gases from the turbine are exhausted through casingl directly through the regenerator 4, thence to the atmosphere throughan exhaust pipe 8. As will be appreciated by those familiar withpowerplants of this type, the turbine rotor is coupled directly so as todrive the compressor rotor, the common rotor shaft being indicated at inFig. l. The useful net power output may be absorbed by any suitable loaddevice, such as an electric generator, pump, or other device (notshown), connected to the end portion 5cl, of the rotor shaft.

A suitable fluid fuel, for instance natural gas, diesel oil, or theheavier residual oils known to the trade as Bunker C, are supplied tofuel nozzles lil, there being one nozzle in each of the combustors 2a.Fuel may be drawn from a storage tank il by a pump indicateddiagrammatically as a positive displacement gear type pump i2, passedthrough a regulating device indicated at i3, which supplies fuel tonozzles il) by way of a conduit ifi in accordance with the position of amanual throttle handle l 5. For the sake of simplicity, the throttle l5is shown to have an ofi position, idle position, and full load position.The precise mechanism by Which fuel regulator i3 performs its functionsis not necessary to an understanding of the present invention;therefore, it is not disclosed more fully herein. It may be noted.however, that this regulator may take many forms, for instance thatdisclosed in the copending application of N. E. Starkey, C. B. Lewis,and M. Edwards, Serial No. 84,416, filed March 30, 1949, now Patent No.2,558,592, and assigned 5to the same assignee as the presentapplication. `Like wise the fuel nozzles I0 may be of the type disclosedin the copending .application of 13.0. Buckland and D. C. Berkey, Serial1'No. l$2,634, led November 30, 1948, now Patent'No. 2,595,759, and alsoassigned to the same assignee.

For starting the powerplant, a suitable auxiliaiy starting motor isrequired to bring the rotor shaft 9 up to the speed required to lire the`combustion system. This starting motor is -indicated at I6 as being anelectric motor fcon- `nected by suitable gears II to drive the rotorponents of the powerplant includes an actuating 'member adapted to bepositioned, either manuvally or automatically by suitable timingdevices, in order to effect the starting and stopping method describedherein. This main actuating mein- `ber is illustrated diagrammaticallyas being a shaft I9 having positioning means represented by the manualhandle having o ff, re, and run positions. As indicated in Fig. 1,moving 'this lever from the off position clockwise toward the runposition causes the starting motor I6 to accelerate the powerplant rotorshaft T9 to a speed at which the compressor will supply air to thecombustion system adequate for initiating combustion. The electriccontroller which performs the various functions required to -make motorI6 start and accelerate the rotor 9 in the desired manner is indicatedgenerally at 2|, and may be anysuitable type of electric motorcontrolling device, the details of which are not material to anunderstanding of the present invention. l

-An extension of shaft I9 is also arranged to actuate control means fortheglow plug or spark plug 24 used to effect ignition in the combustorsThis is represented 4by a contact arm 22 'adapted to rotate with theshaft I9 so as to bridge the ignition circuit contacts 23 when manuallever 20 is moved to the nre position. It will be apparent from Fig. 1how this arrangement completes the circuit from the source of electricalenergy to the spark plug 24. It will also be apparent that when lever 20moves past the fire position into the run position, the ignition circuitis de-energized.

The circuit for controlling the starting motor I6 includes two automaticdevices, one a pressure responsive switch 25 sensitive vto the dischargepressure in the compressor casing Ib,`the other a thermal relay 26actuated by a temperature responsive device indicated diagrammaticallyas being a bimetallic strip thermostat indicated generally at 21.

The pressure switch 25 maybe of any suitable type, but is indicateddiagrammatically in Fig. 1 as comprising a flexible bellows 25a biasedto collapsed position by an internal tension spring 25h and adapted tobe-expanded by compressor discharge pressure communicated by a pressuresensing conduit 25o. The movable endof bellows 25 is pivotally connectedto a contact lever 25d arranged to open contacts 25e when compressorVregulating throttle lever Ib'.

4 discharge pressure rises 'to 'the .normal rated value.

The thermal relay 26 comprises a contact lever 26a adapted to opencontacts 2Gb when biased to the open condition by spring 26C. Lever 26amay be provided with a push-button for manually resetting contacts -26bto the closed condition, in which position lever 26a is retained by apivoted latch 26d, which is in turn biased toward latched position by aspring 26e and arranged to be retracted'by a solenoid 26j when thecircuit there- `to is completed by the closing of the contacts 21a ofthe thermostatic device 21. As will be apparent in Fig. 1, and forreasons which will become apparent from the description of the method ofoperation disclosed below, the circuit from `the `source of electricenergy to ithe solenoid 26j is not completed except when the manuallever 20 is in the run position, in which leverlbridges `the contacts28.

tempting to start the powerplant, it is first necessary to reset thethermal Arelay 26 by means of the manual push-button on lever 2id. By

'thus causing the lever Za to move clockwise about its pivot, thecam-shaped end of Vlatch lever 25d causes the latch kto rotate clockwiseagainst the bias of spring V26e until contact lever 26a reaches theposition where the contactsb are closed, whereupon the latch lever 26esnaps to the engaged position shown in Fig. l, to retain contacts 26hclosed until the solenoid 26j is energized.

It will be apparent from Fig. 1 that with the pressure responsivecontacts 25e and the thermal relay contacts V2Gb both closed, thecircuit to the starting motor I6 is complete so that the motorcontroller2 I is free to energize the starting motor as the operatinghandle 2U is moved away from the off position. It will also be observedthat the bimetallic strip 2lb is in the cold position, with the contacts21a. closed. However, the circuit to the solenoid 25j is open at thecontacts 28.

II' now the motor controller handle 26 is caused to move away from the"ofI" position in the accelerate" direction, the controller 2I energizesmotor I 6 so that the powerpiant rotor shaft S is driven through thegears Ii. 'l'nis motion of handle 2U and the accompanying increase instarting motor speed is indicated by the curve 29 in Fig. 3. By the timethe operating handle 20 reaches the fire position, the speed of rotor 9is such that air is being supplied to the combuston system fromcompressor I at a rate adequate lor supporting combustion. 'l'heignition plug 24 is now energized by reason of the contacts 23 beingbridged by the ignition controller arm 22; and combustion begins. Theluel regulator handle I5 may now be moved away from its off position tothe idle position. As this is done, the fuel supplied to the nozzles Iincreases, as represented by the curve 30 in Fig. 3. The hot gasesresulting from this fuel supplied to the combustion system help toaccelerate the gas turbine rotor; and the motor control handle amarres2D is caused to move progressively to the run position.

As soon as handle E@ moves away from the nre position, the ignitioncircuit to the spark plug 2d is fie-energized, as will be obvious fromFig. 1. It will likewise be apparent that the temperature of theregenerator will begin to rise, with the result that the bimetallicstrip 2lb assumes the curved position indicated by dotted lines in Fig.l, so that the contacts 27a are opened. t will be seen from Fig. 3 thatthe thermal switch 2l opens, due to the temperature rise in theregenerator il, before the motor controller handle 2% reaches the runposition, in which it bridges the contacts 28. Thus the opening of thecontacts in the thermal switch 2 prevents energization of solenoid 251when controller handle 2d moves into the run position.

It is to be noted that the electric starting motor I6 is of a type andcapacity such that it is not capable of turning the powerplant rotor atthe full normal rated speed of the powerplant. For instance, the normalrated speed of rotor shaft S may be on the order of 6700 R. P. M., whilethe starter motor It is designed to bring the rotor up only to a speedon the order of 4G00 R. P. M. This maximum speed condition of thestarting motor, when no fuel is being injected, is indicated by thecurve 29e in Fig. 3, and the further increase in speed of the startingmotor accompanying the motion of the operating handle 2li from the fireto the run position, fuel being supplied by regulator i3, is indicatedby the curve Zea.

Reference must now be made to the nature of the clutch I. This is of theccntrifugally operated sprag type indicated diagrammatically in Fig. 2.lt will be appreciated by those familiar with the power transmission artthat this type of clutch comprises a driving member in the form of arotor ida, having a plurality of cams or ratchet teeth ISE, the drivingrotor Ita being fixed to the shaft of motor IB. The driven member Ic isa disk carrying a plurality of pivwhen the driving rotor I8@ rotatescounterclockwise, the ratchet teeth Ilib engage the end portions ofpawls i3d so that the disk I8@ is positively driven. As the speed of thedriven member increases, centrifugal force tends to throw the pawls i3doutwardly against the bias of the spring ide, which action would, ofcourse, result in disengagement of the pawls from the ratchet teeth.This action is, however, resisted by -reason of the fact that, as longas member Ida is driving disk. ISC, the friction between the ratchetteeth and the ends of the pawls Idd will overcome the tendency ofcentrifugal force to disengage the pawls. rowever, after combustion isinitiated and the turbine 3 begins developing power, while at the sametime the starting motor reaches its maximum speed condition, the torqueapplied by the driving rotor IS@ to the driven motor o progressivelydecreases, and finally the energy developed by the turbine is sufficientto cause the rotor 9 to over-run the driving motor. It will be apparentthat as soon as the driven meinber Ide moves counterclockwise relativeto the driving member Ita, or whenever the torque applied by rotor Illato the driven member ISC decreases to such an extent that frictionbetween 6 ratchet teeth lh and pawl ltd is no longer adequate toovercome centrifugal force, the pawls I8d will fly outward so as to becompletely disengaged from the driving member Ida, and will be retainedin such position during normal operation. Thus there is no wear on theclutch parts in normal running. The point at which the clutch I8disengages is represented by the sharp knee where the ascending speedcurve 29o joins the maximum speed curve 29o (Fig. 3).

As indicated by curve 30 in Fig. 3, further rotation of the fuel controllever I5 causes the speed of rotor 9 to rise to the idling valuerepresented by the curve Sila. This idling speed may be on the order of5400 R. P. M. and, as indicated above, this speed is substantially abovethe maximum speed of the starting motor I6. The design of the pressureswitch 25 is such that it causes the contacts 25e to open at this idlingspeed; therefore, the curve 25e in Fig. 3 shows that the pressure switchopens at the moment the speed of rotor 9 reaches the idling condition.Opening of these contacts breaks the circuit to the starting motor, withthe result that starting motor speed falls along the dotted curve 29e inFig. S. t will be understood that the starting motor controller handle2S remains in the run position so as to bridge the contacts 23, asindicated by the solid curve 29h.

The powerplant is now in normal operation at idling speed, which is thatspeed required to just maintain the gas turbine plant on aselfsupporting basis, but without delivery of any net useful output. Ifthe fuel control handle I5 is now moved from the idling position towardsthe full load position, the additional fuel supplied will result inthedelivery of net output power through the shaft portion da. It mayalso be noted that, in some gas turbine powerplants, the speed at idlingcondition may be equal to the full normal rated speed. In other words,the curve Sila in Fig. 3 would then represent full rated speed,maintained constant by a speed governing device (not shown) on regulatori3, so that further increase in the fuel supply changes the net energyoutput of the powerplant delivered to the load while the fuel regulatorIii maintains rotational speed constant. The broken curve 3019 in Fig. 3represents the normal operation of the powerplant, in which the controllever I5 causes the fuel supply to vary between the idle and full loadconditions.

In shutting down the powerplant, the operation is as follows. The fuelregulator handle I5 is moved to the off position, so that the fuelsupply to nozzles iii is discontinued, as represented by the fallingcurve Sile in Fig. 3. As soon as the fuel is discontinued, the flame isextinguished in combustors 2c and rotor speed begins to drop, with theresult that the pressure switch contacts 25e are permitted to reclose,as indicated by curve 25e in Fig. 3. Since the starting motor controller2li is still in the run position, the closing of contacts 25e causes thestarting motor controller 2l to energize the motor I6 so that it againbrings the powerplant rotor up to the maximum speed of the startingmotor, this restarting of the motor I6 being indicated by the dottedcurve 29d of Fig. 3. Since no fuel is being supplied to the powerplant,motel` I6 will bring the shaft 9 only up to the maximum speed of motorI6 (curve 29e), which, as indicated above, is not sufficient to causepressure switch 25e to open. Air drawn in from the atmosphere is pumpedby the compressor I through the regenerator, :combustion system, turbinevand exhaust casingyso as to remove the storedheattherefrom. Thispositive flow of air alsoresists anytendency theremight be for the windto blow back .through the exhaust casing andcarry heat back to Ythecompressor. .As vthe heat is removed, the bimetallic strip 2lbstraightens out, and contacts21a again close. Thiszcompletes 'the-circuit to the thermal relay solenoid 2612 .with the `result :thatlatch 26d is withdrawn and spring 26c'moves the contactfleverI 26a so asto openthe contactsfZb. This Aagainr de-energizes the starting motor I6,lthe speed of fwhich drops along lthe .curve 29,1* in FiggB.

VSince the'maximum` speed. of the starting. motor is below that requiredvto actuate Athe pressure switch 25, thestartingimotor will run\continuously during the cooling cycle awithoutinterference from ythe pressureswitch? 25.

If it is desired that the .rotor coastlto a standstill before Vthe'starting motor,isrefenergized suitable time :delay mechanism Amay .be.associated with the pressure switch relay 25. VFor purpose of:illustration, this is vrepresented in Fig.

1 as an orifice `2 5f in the pressure sensing 'conduit 25e. 'Instarting, the compressor discharge pressure rises slowly so the orificewill have no appreciable effect on the operation of the relay 25.However, upon shut-down, .the orifice .will tend to .maintain ythepressure 'in bellows 25a, so .the

contacts 25e` do not closel immediately. By: proper design, .the timedelay thus .introduced may be made sufficient topermit. the rotor tocome '.tofrest before themotor I6 is again started.

.After the starting motor has beenstopped by the thermal relay26, it isnecessary, before trying to restart the powerplant, to manually reset.the push-buttonon lever25a to close the contacts 2Gb and re-engage thelatch 26d. Inthis Aconnection it may be noted that' the motor controllerhandle 20 must be returned to the off position before relay 26 willremain reset,.since .aslong as lever 29 is in the run.position the latch26d will be retracted by solenoid 26j with .the result that lever 25aVcannot be reset. This arrangement insures Ythat the motor controllerhandle 20 is in the off position and that the thermal relay 26 isproperly reset before the starting cycle may be reinitiated.

.It will be apparent that the invention thus provides a system for.automatically re-energizing the starting motor in order to y,blow outthestored heat whenever the powerplantisshut down, so as.to'safeguardthe compressor and cthercomponents .against vexcessivevtemperatures Yresulting from thisstoredfheat, as well as preventingdeformation of the rotor during the cooling process.

While the system described above is only semiautomatic, having onemanual controller for the starting motor and a second manualrcontrollerfor the fuel system, `it will be apparentto those skilled in the artthat many modifications vmay be made. It will readily be seen that bothcontrollers l5,,i'l maybe actuated in'proper sequence by a commonautomatic timing arrangement so as to perform theabove-described*processes in the specied sequence. Alsoinanysubstitutions may be made in the control components. For instance,the pressure switch 25 may in some casesbe replaced by any deviceproducing'asignal-asa function-of the speed-of the rotor shaft 9. Thismay-take the'form of a flyballoperated or other-centrifugal speedswitch, or in electric "tachometer -'generator Vproducing avoltage-signal :proportional Ito shaft speed. Likewise the thermalswitch 2'! may be replaced by any-suitable ithermocouple for equivalentdevice capable of producing asignalproportional to the temperaturelofthe regeneratororother principal parts vwhichstore'substantial amountsof heat. Thus thethermaldevice'mayrbe a thermocouple actuatedrelay.responsive,to .the temperature of theregenerator directly, or'to.the turbine temperature orthat inthesturbineexhaust casing. Thelthermal relay itself fcould, of course, take many :other forms rwhichWill readily occurto those'` skilled -in the art.

Aimore complexgas .turbine powerplant embodying the invention, andincorporating Vsome of the modifications suggested abovelisillustrateddiagrammaticallyrin.B*ig.4. .The cycle of operation of'tlsa'powerplantisshown inFig. 5.

This powerplant comprises a low-pressure compressor .3l which'takes-inair from the ambientsatmosphcre through an inlet.3|a'andfdischargesthrough a'conduit132 containingan intercooler '33, `thencethrough a vhighfpressure compressor 3!! communicating by-conduit 35 witha'regeneratorwhch suppliesheated and compressed air through 'thezconduit31 toan annular manifold 33 delivering air-.to the'respectve combustor-s39. :At leastsome'of these combustorscare provided with an ignitingdevice representedbythe sparkv or glowjplug 43; vand-in vthe presentinstance-one combustor isalso provided with a thermal reset switch 4I,the structure and function of which will be described more particularlyhereinafter. .The .combustors .ffurnish hot motive fluid to a two-stageturbine'42 comprising a -rst-stage rotor 42a directly coupledto -drivethe high-pressure compressor S4, second mechanically independent rotorMb directly coupledto the low-pressure compressor 3|. 4Spent motivefluidfrom the turbine is discharged through Van'exhaust casing vt3fcontaininga temperature responsive device indicated diagrammatically as being athermocouple 44. This spent lmotive uid flows through the regenerator33, where some of its remaining heat is transferred to'the'combustionair, after which the/exhaust fluid isdischargedthrough a conduit5.

.With-this arrangement, the second-stage turbine '42h lserves onlytodrive the rvlow-pressure compressor `3|,.and the net power outputisdeliVered through'a shaft 34a by the rst turbine rotor 42a. Thisloadis represented as being a generator 45connected bya `suitable speedreduction gear 4l .to the power'outputshaft i34a.

The fuel system for the-powerplant comprises a suitable pump supplying afluid fuel 4through conduit 48e to an annularmanifold d having branchconduits 48e communicating withthe respective fuel spraynozzles 49, ofwhich there is one in each combustor l39.

For starting this complex powerplant, a plurality of auxiliary primemovers is required First thereis a turning gear motor illustrateddiagrammaticallyat 53 as being a suitableelectric motorconnected througha Lclutch 5| toa pinion .52 adapted to drive the generator gear 53.

`Ahigl'i-pressure starting'motor 54 is connected througha .clutch55 to apinion 55 meshing with the drivegear 34h. .The shaft of pinion 56 isalso arranged to drive the-fuelpump-shaft 48a by means o'f suitablegears48b.

'A third starting motor is shown at .51, connected through a clutch .5.8.to therotor of the 10W-pressure compressor 3 l.

The control system, to which the present invention particularly relates,includes a main controller memb-er represented as the rotary shaft 59adapted to be driven clockwise by a sequence control timing motor ell.This motor is actuated in accordance with a manual controller Si havinga push-button Sla adapted to cause the timing motor K3 to drive theshaft 59 clockwise from its start position to the idle position, and asecond stop button Sie which causes the control shaft Se to rotateclockwise from the stop position back to the start position.

Shaft 5g is arranged to position a number of control components asfollows. The thermal reset contacter 52 comprises a contact segment 52aconnected to rotate with shaft 5d to the bridge contacts b2b so as tocomplete the circuit to the thermal reset switch @I shortly7 after theignition plugs are energized and to complete the circuit across contacts52h throughout acceleration and normal operation, when there is to beflame in the comb-ustors.

The turning gear motor controller E5 is connected by electrical leads63a with the turning gear motor 50 and is adapted to energize this motorin accordance with the sequence of operations described below. Likewisethe high-pressure starting motor controller 64 is connected byelectrical leads lili-a with the high-pressure starting motor 515. Thiscircuit incorporates a thermal shut-off relay 65 comprising a holdingsolenoid 65?' adapted to attract an armature 55k so as to close thecontacts 65e, which are in series with the high-pressure starting motorcontroller Sli and the speed switch contacts c. The thermal shut-orfswitch 55a is arranged to energize the control circuit 5571, for thesolenoid 657'. Switch 65a consists of a cam 55h mounted to rotate withthe shaft 59. This cam is so shaped Ithat initial clockwise rotation ofshaft 59 from the start position immediately causes the cam to engagecontact arm 65e and close the contacts 65j against the bias of spring55d. This energizes the solenoid 65g' and closes the contacts 55e, thuscompleting the circuit from the starting motor controller @t to thestarting motor 54.

Serving the same function as the pressure switch 25 in Fig. l is a speedswitch 'c comprising a contact arm 65a biased by a spring 6513 to closethe contacts 65o at all times except when retracted by a solenoid 56d,which is energized by a tachometer generator 5l coupled to the shaft ofgenerator IES. It will be appreciated by those skilled in the art thatthe tachoineter generator 57 and the circuit Sla connecting it with thesolenoid 55d are so arranged that the solenoid retracts the contact arm65a when the speed of generator 3S reaches a preselected value, andreleases the arm 55a whenever the speed drops below this value.

The low-pressure starting motor controller 68 connected by leads 58awith the low-pressure starting motor 5l. This controller may be arrangedto positively energize and de-energize the starting motor 57 inaccordance with the program illustrated diagrammatically in Fig. 5; oralternatively the circuit 63a may include a speed switch similar torelay 56 and having a solenoid arranged to be energized by tachometergenerator 57i in parallel with the solenoid 65d, so that both startingmotors 54 and 5'! are de-energized in accordance with the speed signalfrom tachometer generator 6l.

The means for controlling the supply of fuel to the spray nozzles 49 isillustrated diagrammatically as being a fuel regulator 69, the detailsof which need not be described here, except to note that this regulatormay be any suitable automatic or semi-automatic device of the generaltype represented by that disclosed in the abovementioned application ofStarkey, Lewis, and Edwards. It will be appreciated by those skilled inthe art that, during normal running, this regulator controls the supplyof fuel in accordance with the load output required of the generator 46.

The igniting device ll is energized at the proper time in the cycle byan ignition controller Hl connected to the spark plug by leads lila.

To guard against the contingency that combustion is not properlyinitiated by the igniting device 4i), means are provided for causing thecontrol system to begin the starting cycle all over in the event burningis not initiated in the combustors 39 promptly after the igniting deviceis energized. This arrangement comprises the thermal reset switch 4l,which includes a fluid-filled bulb lila subjected to the hot gasesinside the combustion space and connected by capillary tube Mb to anexpansible bellows llc arranged to actuate a contact arm lid so astoopen the circuit at the contacts die whenever there is flame in thecombustion space. This thermal reset switch l is in circuit with athermal reset solenoid 7|, which is adapted to automatically actuate thestarting mechanism of the manual control 6I whenever the thermal resetcontactor segment 52a bridges the contacts B2b and the thermal resetswitch arm Md bridges the contacts Me. In this connection it is to benoted that the manual push-button controller 6| is adapted toimmediately return the shaft 59 counterclockwiss to its initialposition, to repeat-the starting sequence, whenever the start buttonlila is actuated. Thus the starting cycle described below is begun anewwhenever the button Bla is actuated manually, or automatically bysolenoid 7l. Thus the starting cycle is repeated whenever ignition failsto occur or when combustion accidentally ceases for any reason.

It should be observed that clutches 5|, 55, and 58 are all of theoverrunning type represented in Fig. 2.

Having described generally the various components cf the controllingmechanism, the sequence of operations will be seen from a considerationof Fig. 5.

With the main controller member 59 in its initial or start position, thethermal reset contactor 652 is in open condition so that the circuit tothe reset solenoid 7| is not completed, even though the thermal r-esetswitch d! is closed by reason of the low temperature in the combustionsystem. The thermal shut-off relay 65 is in open condition, describedabove in connection with Fig. l, and the speed switch 66 is closed,since tachometer generator 61 is putting out no signal. The turning gearmotor controller 63, low-pressure starting motor controller 68, fuelregulator 59, andl ignition controller 'It are, of course, in the oncondition.

To start the powerplant, the push-button Bla is depressed, causing thetiming motor 60 to rotate shaft 59 clockwise away from the startposition. This motion rst causes the thermal reset cam 65h to closecontacts 65j so as to energize solenoid 65g' and complete the circuitbetween the highpressure starting motor controller 54 and the motor 54.Simultaneously the turning gear motor controller 63 energizes the motor5B. The function of this motor, with its very high gear ratio to ith'egeneratordrivegear 53,' is to break therotors' loosef in'. their.Vbearings, extremely high starting` torque being required'to' overcometheY static fric tionin thelarge journalrbearings required in thehigh-pressure compressor 3G, generator Woland.` The motor! 5)Y may.-ybe: of a comparatively smaller;v size. than would be..req1.iired' if; itwere used to break theA The'. capacity of the high-pressure. starting.motorfll :isso selected. that' it is just capable'. of rotating fthehighpres rotors' loose in. their' bearings.

sure compressor rotor at nringspeedmvhch may beon' the order ofv 10% offull rated' speed', which means vthat this will be themaximurn speedwhen motor Skis-driving through the clutch 55, with no helpfrom the.turning gear motor 5E) =or the firststage turbine rotor 42a. It will beappreciated that, if the high-pressure starting rnotor 54- isenergizedslightly before the turning gear motor 50-isde-energized, motor54 will bring the'speedv up-acc'ording to the curvey 12 in Fig. 5', withthe result' that' the turning gear pinion 52'Will oVerrun the-'turninggear motor 5i! and the unidirec'- tionall clutch 5| willv disengage.turning gear motor 50'will continue to run at its synchronousno-loadspeed until de-energized by the-controler 63.

Since it is dangerous to attempt to restart a gas turbine powerplant aslong as there are. explosive gases in the combustion system, turbine,and exhaustpiping, the motor controller 64 is arranged to keep thehigh-pressure starting motor Menergized for a substantial length of timerepresented by the horizontal-portion 13 of the speed curve in Fig. 5.This. operationmay continue for'about foun minutes and' constitutes` apurging cycle,. during which the high-pressure compressor is rotated atsufhcient speed t0 draw air through the low-pressure compressor andrelated piping and blowitthrough the regenerator. combustion system,turbine, and exhaust piping so as to expel any fuel-air mixturewhich'may remain from previous operatingcycles. After this purgingcycle,the -ignition plugs 40 arev energized by the controller 10,and/simultaneously the fuel'regulator. 69 is positioned to beginsupplying` fuel atan increasing rate -to thenozzles 4Q. Thisprogressively increasing supply of fuel is'indic'ated-by the ascendingcurve 14.in Fig. 5.

Attheinstant the fuel supplybegins, theignition controller menergize'sthe plug 1U-and combustion. begins, unlesssome abnormal conditionpreventsthe initiationof flame. If combustion does begin properly,thethermal reset switch 4l is caused to open promptly by the uid'in bulbl l a causing expansion of bellows Ille. Further rotationofr-maincontrol'shaft E9' causes-the ignition controllerto(le-energizethe'plug 4D, at the same. time moving'thethermal'reset-contactor G2 to the closed position.- It will no'w be'apparent that, if the thermal reset switchllfl has not been opened byreason of the initiation' of flame in theV combustion system, thebridging ofthe contacts (52h/by the'contactor' arm 62a' willcomplete thecircuit` to the restart solenoid TI, which then actu- After this, the

ates the. starting button' Sla. Thus shaft 59is quickly returnedcounterclockwise to its initial positionand the timing. motor B0 againbegins driving shaft 59 clockwise so that the complete starting cycledescribed so far is repeated. In the caseof sucha false start, thepurging cycle 13 is of particular.` importance since there would-almostcertainly be an explosion if the spark plugs 40 were. re-energizedwithout rst clearing the system oftheexplosivemixture resulting from therst starting cycle. It willbe apparent that in normal operation.. the.thermal' reset. switch. M opens before the thermal reset contacter 52closes, withthe. result'that the.v restart solenoid 1| isnot energized.`

As fuel supply isincreased according'tothe. curve 14, theturbin'efAZaybegins to assistv in driving the high-.pressure compressor'sdzand'the'genferator'46. However, thethermodynamic cycleof` the .powerplantis'n'otyet.selfsupporting, which.

means thatthe high-pressure'. starting motorA 64 is still supplyingtorque tolthepinion 56,.with the result that clutch. 55 remains.engaged, asA described-above inconnection with the clutch lain Fig.V 1.The' additional torque: supplied by the first-stage turbine rotorA 42aproduces acceleration' ofl the'high-pressure compressor. rotorasindic'ated' by the ascending speed curve'15' in Fig; 5.

Ihexhot motive fluid'discharged from the rststage. turbine; 42a now, ofcourse, begins to supply' energy to. the' second-stage rotor 42h'. Thefunctionoi the low-pressure' starting motor 51 is to assistv in bringingthe' low-pressure. compressor speed up moreA rapidly to its-normal ratedcondition. To this end,.the low-pressure starting. motor controller 68-lenergizes motor 5'!A shortly after combustionis initiated. It will beunderstood' that motor. 51 continuesto supply'v torque tothe.low-pressure compressor rotor.' untilsuch tirneas the second-stageturbine wheel 152i)A disengages clutch 58 by causing thelowpressurercompressor rotor to over-run the lowpressure starting motor5.1, or until the lowpressure controller SSde-energizes motor 51. Iftheclutch- -'shoulddisengage before motor 51 is de-energized,v the motorwill' simply operate at its synchronous speed until the controller 68does shut it down.

It may be noted' that' the raised dwell of cani Gbis of such a lengththat the thermal shut-off contacts 653" are positively held closed untilafter the'ignition plugs are energized and combustionbegins. The-hotgases then cause the thermocouple 44' to put out. an increasing signalwhich is multiplied in. the amplifier 44a.. This signal causes theholding solenoid g to mainl tain contact arm 65e in the closedposition'. Thus as long asthe powerplant is hot, the ther'- mocoupleMacts to keep solenoid 65g energized and the contacts 65e closed. Duringnormal running operation, the circuit' tothe starting motor 54'will'beopened'by the operation of the speedswitch 66', as noted below. Duringnormal operation and during' the stopping cycle, the cam' 65h isdisengagedfrom the Contact arm 65o so that the contacts 65j will beopened by spring 65d, whenever the temperature signal from.the'thermocouple 44 decreases sufficientlyV to indicate that thetemperature level of the powerplant is down to a safe value.

With further increase in the fuel supply, the rotor speed of thegenerator 46 increases until tachometer generator 61 produces a signalvoltage'. adequate toY energize solenoid 66d and open theispeed switchcontacts 66e. This causes the high pressure starting motor 54 to be shutdown. In order to make sure that the high-pressure starting motor willremain energized as long as it still needed to supply torque to thepinion t, the speed switch 66 is so arranged that it does not open untilafter the Clutch 55 disengages by reason of the rst-stage turbine rotorover-running the high-pressure starting motor. The point at which clutch55 disengages is indicated by the sharp knee in the curve l5 in Fig. 5.After this point, the motor 54 continues to run at its synchronous speeduntil de-energized by opening of the speed switch 65. This synchronousrunning is represented by the level part 'l of the curve in Fig. 5. Whenthe speed switch 66 de-energizes motor 55, its speed drops along thecurve 11.

Continued rotation of the control shaft 59 causes the fuel regulator tobring the powerplant up to idling speed, represented by the horizontalportion of the curve 'i8 in Fig. 5. When shaft 5s reaches the idleposition, sequence motor 50 automatically stops. Thereafter, normaloperation of the powerplant at loads varying from idle to full, asdictated by the fuel regulator 65, is indicated by the broken curve i9.

The stopping cycle of the powerplant is as follows. When the stop buttonGib of the manual control el is actuated, the timing sequence motor Si]begins to drive the shaft 59 clockwise through the remaining portion ofits revolution, as shown on the indicator dial 59a in Fig. 4. Thisimmediately causes the fuel regulator S9 to out off the supply of fuelentirely, with the result that the fuel supply falls to zero, asindicated by the curve 88. Simultaneously, the decreased signal from thetachometer generator 5l causes the solenoid 55d to release the contactarm 56a so that the contacts @Sc are closed to again complete thecircuit from the highpressure starting motor controller 66 to the motor5e. Continued rotation of shaft 59 now causes the high-pressure startingmotor controller 55 to accelerate the starting motor 54, as indicated bythe ascending curve 8l in Fig. 5. Since no fuel is supplied and theignition plugs are not energized in this portion of the cycle, the motor5A accelerates to the maximum speed at which it is capable of drivingthe highpressure compressor Sil. This maximum speed of which thestarting motor 54 is capable when driving the compressor 3d without aidfrom the turbine is represented by the horizontal curve S2 in Fig. 5.Since this is considerably below the idling speed, at which the speedswitch EE opens the starting motor circuit, the motor 5d will continueto drive the compressor 34, as indicated by the curve 82.

Continuing rotation of compressor 34 by the high-pressure starting motor54 pumps air through the entire powerplant and carries away the storedheat in the regenerator, turbine, combustion system, etc. Rotation ofthe compressor and turbine rotor during this cooling process alsoinsures that the rotors will cool evenly.

As the temperature of the powerplant falls, the output of Jrhermocouple44 decreases until ultimately it is insufficient to enable the solenoid65g to hold contacts 55j closed. The result is that spring 65d opens thecontacts 65j, thus breaking the circuit to the holding solenoid 657'.Contacts 55e now open, thus breaking the circuit to the starting motor54, the speed of which falls along the curve 83 in Fig. 5.

This purging and cooling cycle may be somewhat shorter than the totaltime required for the sequence motor 60 to return shaft 59 to the startposition. It will, of course, be appreciated by those skilled in the artthat the thermal shutoff relay 55 and the thermal shut-olf switch 65aand the associated thermocouple @Il could be dispensed with and thesequence controller motor @il be employed to return the high-pressurestarting motor controller 65 to the ofi condition when shaft 59 returnsto the start position. It is, of course, more economical of the electricpower consumed to have a thermal device shut down the starting motor assoon as the temperature of the powerplant decreases to a safe value. Inany event, the timing motor 55 will return the shaft 59 to the startposition and then automatically stop, ready for the next operatingcycle.

Thus it will be seen that the control system of Fig. 4 performs in amore automatic fashion the same purging and cooling process describedabove in connection with Fig. l. It will be appreciated, of course, thatall the functions of the system of Fig. 4 might be performed byanalogous manual operating devices.

In addition to the alternative components suggested above, many otherchanges and modifications will occur to those skilled in the art; and itis desired to cover by the appended claims all such changes as fallwithin the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. In a regulating system for a gas turbine powerplant having anauxiliary prime mover connected to drive a compressor for furnishing airto the combustion system, the combination of means for automaticallyrestarting the auxiliary prime mover to drive the compressor when thefuel supply to the combustion system is discontinued, and means forstopping the auxiliary prime mover in accordance with a temperaturecondition in the powerplant.

2. In a regulating system for an open cycle gas turbine powerplanthaving an auxiliary prime mover adapted to drive a compressor forfurnishing air to the combustion system, the combination of means forautomatically restarting the auxiliary prime mover to drive thecompressor when the speed of the powerplant rotor drops below apreselected value when the powerplant is shut down, whereby air from theambient atmosphere is pumped through the powerplant to carry away heatstored in the hot components thereof, and means responsive to atemperature condition in the powerplant for stopping the auxiliary primemover when the stored heat has been substantially removed.

3. In a regulating system for an open cycle gas turbine powerplanthaving at least one turbine-compressor and an auxiliary starting motoradapted to bring the compressor rotor up to firing speed during hestarting cycle, the combination of means for automatically restartingthe motor for driving the compressor rotor when the fuel supply to thecombustion system is discontinued, whereby cool air from the ambientatmosphere is pumped through the powerplant to carry away heat storedtherein, and means for stopping the motor when the temperature of thepowerplant is reduced to a preselected value.

4. In a regulating system for an open cycle gas turbine powerplanthaving at least one turbine-compressor and an auxiliary starting motorconnected to bring the compressor rotor up to firing: speed', duringthe; startingcycle, the4 combination; of means for automaticallyrrestarting the motortov drive thecompressorV rotor when the.

speed. thereof falls below the ring speed when the. powerplant is shutdown, whereby air from the. ambient atmosphereis pumped through thepowerplant; to remove. heat stored therein, and means for automaticallydisconnecting thestartingmotorfwhen the temperature of a hot.componentof the powerplant is reduced to a preselectedi value.

5.'.In; a regulating system for an open cycle gas: turbine; powerplanthaving at least one turbine-driven. compressor, a heat exchanger havingsubstantial heatstorage capacity, and an auxiliary startingmotorgadapted tobringthe turbinecompressor rotor: up to firing speedduring, the startingcycie, thecombination ofmeans responsive;l to 1rotor-speed' for automatically de-energizngthe4 motor; at` thecompletion of. the starting` cycle, means for automatically restartingthe motor 'to drive the turbine-compressor rotor whenV thefspeedVthereof falls below a preselected value, whereby air is. pumped throughthe powerplant to remove heat stored inV theheat exchanger, andY means.responsive. to the temperature of said'cooling airA for automaticallystopping the motor when the stored heatis substantially removed fromtheheat, exchanger.

6; In a regulating system for a gas turbine powerplant having at least'one turbine-driven compressor, aheat; exchanger having substantial heatstorage capacity; and an auxiliary prime mover adapted to bring thecompressor rotor up to firing speed during the starting cycle, thecombination of means for automatically disconnecting the auxiliary primemover at the completion of the startingY cycle, means for automaticallyrestarting said prime mover to drive the compressor rotor when thepowerplant is shut down, whereby air is pumped through the powerplant toremove heat stored in the heat exchanger', and means responsive to atemperature condition in the. powerplant for automatically disconnectingthe prime mover when the stored heat issubstantially removed from theexchanger.

7. In a regulating system for an open cycle gas turbine powerplanthaving at leastV one turbinecompressor, a combustion system with meansfor supplying fuel thereto, and an auxiliary starting motor. adapted tobring the compressor rotor up toring speed during the starting cycle,the combination of means for disconnectingthe starting motor when thespeed of the compressor rotor rises to` a. preselected value abovefiring speed, means for automatically reconnecting the startingmctor todrive the compressor rotor when the speed thereof drops below saidpreselected value, whereby air is pumped through the powerplant to carryaway heat stored therein when the supply of fuel to the combustionsystem is discontinued, and means for automatically disconnecting thestarting motor when said stored heat is substantially removed;

8. In a regulating system for an open cycle gas turbine powerplanthaving at least one turbinecompressor and a combustion system with meansfor supplying fuel thereto and an auxiliary starting motor adapted tobring the compressor rotor up to firing speed during the starting cycle,the combination of means for disconnecting the starting motor when thedischarge pressure of the compressor rises toa preselected value, meansfor automatically reconnectingI the starting motor to drive. the.compressor when the discharge pressure I6 thereofdropssubstantiallybelow said preselected value, whereby cool air from the ambientatmosphere. is pumped throughA the powerplant to remove heat storedtherein when the powerplant is shut down, and means for automaticallydiscontinuing operation of the starting motor when said storedheat issubstantially removed.

9. In a regulating system for an open cycle gas turbine powerplanthaving at least one turbinecompressor with a combustion system and meansfor delivering fuel thereto and a starting,r motor adapted to bring thecompressor rotor up to firing speed during. the starting cycle, thecombination of means for automatically discontinuing operation of thestarting motor when the speed of the turbine-compressor rotor rises to apreselected value, means for again connecting the startingmotor to drivethe turbine-compressor rotor when theY speed thereof; dropsy upondiscontinuance of fuel supply to the combustion system, wherebycomparatively cool air from the ambient atmosphereiis pumped through thepowerplant to purge residual fuel vapors and remove heat stored in thehot components of the powerplant, and means for automaticallydiscontinuing operation of the starting motor when the temperature ofsaid hot components is reduced to a preselected value.

10. In a regulating system for an open cycle gas turbine powerplanthavingan auxiliary prime mover adapted to drive a compressor forfurnishing air to the combustion system, the combination of means forautomatically restarting the auxiliary prime mover to drive thecompressor when the supply of fuel to the combustion system isdiscontinued upon shut-down, whereby air from the ambient atmosphere ispumped through the powerplant to carry away heat stored in the hotcomponents thereof, and means for automatically stopping the compressorwhen said stored heat has been substantially removed.

11. In a regulating system for a gas turbine powerplant having at leastone turbine-compressor with a combustion system and means fordelivel-ingI fuel thereto and an auxiliary prime mover adap-ted to beconnected to bring the compressor rotor up to ring speed during thestarting cycle, the combination of means for automatically disconnectingthe auxiliary prime mover from the compressor when the speed of theturbine-compressor rotor rises to a preselected value during thestarting cycle, means for automatically re-connecting the auxiliaryprime mover to drivev the compressor when the supply of fuel to thecombustion system is discontinued upon shutdown, whereby comparativelycool air is pumped through the powerplantv to remove heat stored in thehot components thereof, and means for automatically disconnectingtheauxiliary prime mover when said stored heat is substantially removed.

GEORGE R. FUSNER. CHAPMAN J. WALKER.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES. PATENTS Number Name Date 2,129,529 Howard Sept. 6, 19382,252,456 Buehman Aug. 12, 1941 2,443,648 Austin et al June 22, 19482,538,179 Weinhardt .Jan. 16, 1951v

